How to Zoom In and Zoom Out In Browser

Have you someday find web pages that you think the letters are too small, even though the information is you need.
Or you find a page with letters so big that you feel uncomfortable to read. or is there a slight problem with your eyes ..
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To make it convenient, we just zoom in or zoom out by using a keyboard shortcut.

The command to zoom in or zoom out, same on all browsers (Mozilla Firefox, Opera, Safari, Chrome)
namely:

Press Ctrl + + to zoom in
Press Ctrl - to zoom out
Press Ctrl 0 to return to its original size.